The present invention relates, in general, to a rotor structure for an electric motor and to a method of manufacturing such a rotor structure.
Typically, an electric motor has a rotor structure with a cylindrical rotor core assembly having an end surface, a plurality of permanent magnets disposed on the outer circumference of the rotor core, and a bandage wrapped around the rotor core assembly to radially secure the permanent magnets on the outer circumference of the rotor core assembly. One end of the bandage is arranged in proximity of the end surface and should be carefully attached to the rotor to prevent a detachment from the rotor, when the rotor operates at high circumferential speeds, for example 170 m/s.
One approach to affix the end of the bandage to the circumference of the rotor involves the use of an adhesive tape to secure the bandage end and subsequently to apply an additional 1.5 layers of adhesive tape for added safeguard. The final fastening of the bandage is realized by soaking the bandage in epoxy resin and subsequent thermal curing.
However it has been shown that adhesive forces between the tape and subjacent layer or layers of the bandage are not always sufficient, so that the bandage end becomes detached. As a consequence of a detachment of the bandage end, contact may occur with the wall of the stator bore during operation of the motor, resulting not only in ultimate destruction of the bandage, but also in heating of the motor and grinding noises during motor operation. Moreover, the detachment of the tape or bandage may also lead in a loss of pre-tension by which the bandage has been assembled, so that the force with which the permanent magnets are affixed to the rotor core is reduced.
The detachment of the bandage end or the end windings of the tape results in all likelihood to the destruction of the bandage, or at least to an impairment and losses. As a large-scale production does not enable a test of the adhesive strength without destruction of the tape, the actual testing of proper securement of the bandage is limited to visual inspection. Therefore, it is of utmost importance to make sure that the end or ends of each bandage is/are securely attached.
It would therefore be desirable and advantageous to provide an improved method to obviate prior art shortcomings and to ensure a secure attachment of a bandage end for a rotor to outer permanent magnets.